Wide angle zoom lens system

ABSTRACT

A wide angle zoom lens system comprising, in order from the object side, a first positive lens unit, a second positive lens unit and a third negative lens unit; and configured so as to perform variation of focal length by varying airspaces reserved between these lens units. The first lens unit consists of a negative front subunit and a rear positive subunit. The zoom lens system has a wide field angle and favorable optical performance.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to zoom lens system which has a wide fieldangle.

b) Description of the Prior Art

In the present days, there is a remarkable trend manufacture, ascommercial products developed with a new concept, fully automatedcameras which incorporate zoom lens systems having high vari-focalratios. These zoom lens systems having high vari-focal ratios alwayshave wide field angles or high telephoto ratios.

The conventional zoom lens systems have field angles on the order of 2ω=63° at wide positions thereof. Further, out of zoom lens systems whichhave low vari-focal ratios, there are known those which have fieldangles on the order of 2 ω=84° as exemplified by the zoom lens systemdisclosed by Japanese Patent Kokai Publication No. Hei 2-284,109.

Further, conventional super wide angle zoom lens systems are known onlyas interchangeable lens systems which are to be used with single-lensreflex cameras. However, the lens system proposed by Japanese PatentKokai Publication No. Hei 2-135,312 is a compact zoom lens system whichis usable with lens shutter cameras.

Each of the lens systems mentioned above cannot correct aberrationssufficiently favorably since it was obtained simply by modifying anexsisting zoom lens system so as to have a wider field angle. In otherwords, each of the zoom lens systems mentioned above is a telephoto typezoom lens system which is modified so as to have a shorter focal lengthor a wider focal length and is insufficient in optical performancethereof.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a zoom lenssystem which comprises three or four lens units, and is configured so asto have wide field angles, large apertures and aberrations correctedfavorably by selecting an adequate composition for a first lens unit outof the lens units.

The zoom lens system according to the present invention comprises, inorder from the object side, a first lens unit having positive refractivepower, a second lens unit having positive refractive power and a thirdlens unit having negative refractive power; is configured to performvariation of focal length by varying an air-space reserved between thefirst lens unit and a second lens unit as well as an airspace reservedbetween the second lens unit and a third lens unit; and is characterizedin that the first lens unit consists of a front subunit and a rearsubunit, and satisfies the following condition (1):

    |φ.sub.f φ.sub.1 |<6.0           (1)

wherein the reference symbols φ_(f) and φ₁ represent refractive power ofthe front subunit and refractive power of the first lens unitrespectively.

The zoom lens system according to the present invention has beenobtained by widening the field angle and further improving opticalperformance of the lens system proposed by Japanese Patent KokaiPublication No. Hei 2-135,312. Speaking concretely, the field angle ofthe lens system disclosed by the above-mentioned patent has been widenedreasonably by shortening a total length of the lens system, selectingthe above-described type of zoom lens system which comprises the threelens units, in order from the object side, a first lens unit havingpositive refractive power, a second lens unit having positive refractivepower and a third lens unit having negative refractive power, andcomposing the first lens unit so as to be suited for widening the fieldangle of the lens system.

Japanese Patent Kokai Publication No. Hei 3-208,004 proposed a zoom lenssystem as an improvement of the above-mentioned lens system tofacilitate correction of aberrations and widen the field angle thereofby reserving an airspace wider than a certain value between a negativelens component and a positive lens component composing the first lensunit without modifying a composition of this lens unit itself so as toreduce an angle of incidence of the offaxial ray on the second lens unithaving positive refractive power.

In contrast, the zoom lens system according to the present invention hasa field angle widened by adopting a composition of the first lens unitwhich is modified so as to be suited for widening the field angle of thepreceding lens system as a whole. In other words, the zoom lens systemaccording to the present invention has been obtained not on the basis ofa fundamental composition of the above-mentioned zoom lens system havingthe widened field angles, but on the basis of a fundamental compositionof the preceding zoom lens system which has an entire zooming range froma wide position to a tele position or a range of field angles which isconvenient for designing a zoom lens system and by shifting thecomposition toward the wide position.

Speaking concretely, it is possible to obtain, for example, a zoom lenssystem having a range of focal length f from 28 mm to 105 nun bydesigning first a zoom lens system having focal length f from 35 nun to135 mm and equipping this zoom lens system with an attachment lenssystem for widening field angle by shortening the focal length f 0.8 ×as long. When the zoom lens system which is adopted as the basis has ashort total length f and a small outside diameter, the addition of theattachment lens system for widening the field angle to the zoom lenssystem does not enlarge so much the zoom lens system as a whole.

When a single zoom lens system is composed by building the attachmentlens system for widening field angle in the zoom lens system adopted asthe basis, this attachment lens system can be considered as a lens unitor a lens component which is used for correcting aberrations. That is tosay, the attachment lens system which is originally adopted as aseparate afocal converter can be regarded as a lens unit or a Lenscomponent which is used for widening the field angle of the zoom lenssystem.

In the zoom lens system according to the present invention, this lenscomponent is used as a front subunit L_(a) in the first lens unit andthe first lens unit of the zoom lens system adopted as the basis is usedas a rear subunit L_(b) of the first lens unit of the zoom lens systemaccording to the present invention. That is to say, the zoom lens systemaccording to the present invention is of a retrofocus type in which afirst lens unit is composed of a wide angle afocal converter (the frontsubunit) and a positive subunit (the rear subunit), and an airspacereserved between these subunits is narrowed for making the zoom lenssystem compact.

On the basis of the concept described above, the zoom lens systemaccording to the present invention comprises the three or four lensunits as described above.

Further, in order to accomplish the object of the present invention, thezoom lens system according to the present invention is configured so asto satisfy the above-mentioned condition (1).

The object of the present invention is to provide a wide angle zoom lenssystem which has a field angle 2 ω, for example, of approximately 63° orlarger at a wide position thereof as described above. For obtaining thezoom lens system having a wide field angle, the type and composition ofthe conventional zoom lens system are not modified. When the field angleof the conventional zoom lens system is to be widened without modifyingthe type thereof, heavier burdens for correction of aberrations, etc.are imposed on the third lens unit, thereby making it impossible toreserve a sufficient back focal length at the wide position of the zoomlens system. Further, a heavier burden for obtaining a requiredmagnification at a tele position is imposed, thereby making it difficultto correct aberrations and obliging to use surfaces which can hardly bemanufactured in practice.

Furthermore, aspherical surfaces and graded refractive index lenselements cannot be manufactured easily in practice though it isconceivable to use aspherical surfaces and graded refractive index lenselements for correcting aberrations.

In an attempt to widen a field angle of a zoom lens system, differencein optical path between the paraxial ray and the offaxial ray in thelens system makes it difficult to correct aberrations. In other words,curvature of field, distortion, sagittal flare due to coma, etc. areaggravated as a zoom lens system has a wider field angle.

For the reason described above, the present invention selects a zoomlens system comprising the three lens units as the basis as alreadydescribed above and adopts a nearly symmetrical composition wherein anaperture stop is arranged in the middle of a second lens unit forobtaining a zoom lens system which is advantageous for correction of theaberrations. Even when the location of the aperture stop is shiftedforeward or backward, the fundamental composition of the zoom lenssystem remains unchanged though the zoom lens system uses a differentportion of a light bundle.

After adopting the nearly symmetrical composition which is advantageousfor correction of the aberrations, lens components to be used for thezoom lens system are modified so as to be suited for widening the fieldangle of the conventional zoom lens system. Since the type selected forthe zoom lens system according to the present invention permitsshortening a back focal length of a lens system, the type makes itpossible to shorten a total length and reduce an outside diameter of thelens system. That is to say, the zoom lens system according to thepresent invention is configured by selecting the composition which issymmetrical with regard to an aperture stop as the basis and usingadditional lens component(s) which is adopted for shortening the fieldangle of the conventional zoom lens system. In the zoom lens systemaccording to the present invention, the front subunit serves forcompensating for functions of the rear subunit in the first lens unit.Judging from rays passing through the first lens unit and the third lensunit in the zoom lens system according to the present invention,offaxial aberrations are largely influenced by the second lens unit andthe third lens unit, whereas axial aberrations, mainly sphericalaberration, are greatly influenced by the second lens unit.

Moreover, in order to obtain a zoom lens system having a wide fieldangle, it is necessary to correct aberrations such as lateral chromaticaberration and distortion having an inflection point which are inherentin a wide angle lens system. That is to say, it is necessary for thezoom lens system according to the present invention to pay attention tocompositions of the first lens unit and the third lens unit in order tocorrect the aberrations inherent in a zoom lens system having a widefield angle and pay attention to composition of the second lens unit inorder to obtain a high aperture ratio.

For the wide position of the zoom lens system according to the presentinvention, it is not advantageous to compose the thrid lens unit of aremarkably increased number of lens components. Since a powerdistribution which locates a rear principal point after a lens system isselected for the zoom lens system according to the present invention,reservation of a required back focal length is more difficult than thecorrection of the aberrations for the zoom lens system according to thepresent invention, thereby lowering freedom of the correction of theaberrations for this zoom lens system. Accordingly, it is preferable tocompose the third lens unit of a small number of lens components byusing an aspherical surface. The use of the aspherical surface makes itpossible to reduce aberrations remaining in the third lens unit itselfand correct aberrations of high orders produced in the first lens unit,thereby permitting correcting aberrations with good balance in the zoomlens system as a whole. Further, the use of the aspherical surface makesit possible to reserve a required back focal length reasonably, preventa rear lens element from having a prolonged diameter, and reduce flareto be produced by an inside surface between a film surface and the rearlens element.

When the points described above are taken into consideration, it isdesirable to contrive the first lens unit so as to correct the lateralchromatic aberration and distortion of high orders which are inherent inthe wide angle zoom lens system.

In the vicinity of the wide position of the zoom lens system whereinparticularly the offaxial ray is high, it is difficult to correct theresidual aberrations of high orders by the second lens unit and thethird lens unit when the aberrations are not corrected sufficiently inthe first lens unit. This fact is apparent from tables of aberrationcorrection coefficients shown below. Checks of balance betweenaberrations of high orders and aberrations of low orders is especiallysignificant.

Tables 1 and 2 shown below clarify conditions of the aberrationscorrected by aberration coefficients which are selected in a firstembodiment of the present invention to be described later.

                                      TABLE 1                                     __________________________________________________________________________    Wide position                                                                 __________________________________________________________________________        K  SA3   CMA3 AST3 DIS3 PTZ3                                              __________________________________________________________________________        1  -0.00001                                                                            -0.00060                                                                           -0.00634                                                                           -0.68756                                                                           -0.01525                                          Lf  2  0.00393                                                                             -0.00302                                                                           0.00026                                                                            -0.01807                                                                           0.07043                                               3  -0.00388                                                                            -0.00784                                                                           -0.00176                                                                           -0.03585                                                                           -0.05142                                              4  0.00011                                                                             0.00380                                                                            0.01529                                                                            0.35334                                                                            0.01401                                               5  0.00000                                                                             0.00004                                                                            -0.01272                                                                           -0.66454                                                                           0.01346                                               6  0.01626                                                                             0.00255                                                                            0.00004                                                                            0.00360                                                                            0.06885                                           Lb  7  -0.01313                                                                            -0.01030                                                                           -0.00090                                                                           -0.01394                                                                           -0.05240                                              8  0.00030                                                                             0.00926                                                                            0.03159                                                                            0.29145                                                                            -0.00313                                              9  -0.00643                                                                            -0.01924                                                                           -0.00639                                                                           -0.06723                                                                           -0.06106                                              10 -0.00041                                                                            0.01420                                                                            -0.05513                                                                           0.88004                                                                            -0.02043                                          (1)                                                                             Lf   0.00016                                                                             -0.00765                                                                           0.00744                                                                            -0.38814                                                                           0.01777                                             Lb   -0.00341                                                                            -0.00348                                                                           -0.04350                                                                           0.42938                                                                            -0.05471                                          (2)    -0.00568                                                                            -0.00308                                                                           0.11297                                                                            -0.99783                                                                           -0.10148                                          (3)    0.00164                                                                             0.00491                                                                            -0.07868                                                                           0.54632                                                                            0.13018                                           __________________________________________________________________________        K  SA5   CMA5 AST5 DIS5 PTZ5 SA7                                          __________________________________________________________________________        1  0.00000                                                                             0.00000                                                                            0.00089                                                                            0.19925                                                                            0.00537                                                                            0.00000                                      Lf  2  0.00005                                                                             0.00010                                                                            -0.00019                                                                           -0.04197                                                                           -0.02465                                                                           0.00000                                          3  -0.00006                                                                            -0.00030                                                                           0.00309                                                                            0.05851                                                                            0.02059                                                                            0.00000                                          4  0.00000                                                                             0.00001                                                                            -0.00278                                                                           -0.17371                                                                           -0.00664                                                                           0.00000                                          5  0.00000                                                                             0.00000                                                                            0.00140                                                                            0.29779                                                                            -0.00517                                                                           0.00000                                          6  0.00045                                                                             0.00065                                                                            -0.00128                                                                           -0.06874                                                                           -0.03299                                                                           0.00001                                        Lb                                                                              7  -0.00038                                                                            -0.00086                                                                           0.00385                                                                            0.06245                                                                            0.02784                                                                            -0.00001                                         8  0.00001                                                                             0.00015                                                                            -0.00667                                                                           -0.24618                                                                           -0.00634                                                                           0.00000                                          9  -0.00013                                                                            -0.00038                                                                           0.00605                                                                            0.10153                                                                            0.03024                                                                            0.00000                                          10 -0.00001                                                                            0.00027                                                                            -0.00851                                                                           -0.05951                                                                           0.00708                                                                            0.00000                                      (1)                                                                             Lf   -0.00001                                                                            -0.00019                                                                           0.00100                                                                            0.04207                                                                            -0.00532                                                                           0.00000                                        Lb   -0.00006                                                                            -0.00017                                                                           -0.00516                                                                           0.08734                                                                            0.02066                                                                            0.00000                                      (2)    0.00215                                                                             0.00210                                                                            0.02325                                                                            0.11002                                                                            0.04238                                                                            0.00044                                      (3)    -0.00011                                                                            -0.00182                                                                           -0.01764                                                                           -0.23535                                                                           -0.04339                                                                           -0.00001                                     __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Tele position                                                                 __________________________________________________________________________        K  SA3   CMA3 AST3 DIS3 PTZ3                                              __________________________________________________________________________        1  -0.00012                                                                            -0.00129                                                                           -0.00153                                                                           -0.02522                                                                           -0.00533                                              2  0.07407                                                                             -0.15959                                                                           0.03821                                                                            -0.04511                                                                           0.02461                                               3  -0.07297                                                                            0.12950                                                                            -0.02554                                                                           0.02573                                                                            -0.01796                                              4  0.00198                                                                             0.00570                                                                            0.00182                                                                            0.00645                                                                            0.00489                                               5  0.00000                                                                             0.00011                                                                            -0.00449                                                                           -0.02568                                                                           0.00470                                               6  0.30610                                                                             -0.62100                                                                           0.13998                                                                            -0.11093                                                                           0.02405                                               7  -0.24715                                                                            0.48029                                                                            -0.10370                                                                           0.07903                                                                            -0.01831                                              8  0.00567                                                                             0.01211                                                                            0.00287                                                                            0.00127                                                                            -0.00109                                              9  -0.12109                                                                            0.19893                                                                            -0.03631                                                                           0.03156                                                                            -0.02133                                              10 0.00765                                                                             0.05210                                                                            -0.03943                                                                           0.10570                                                                            -0.00714                                          (1)                                                                             Lf   0.00296                                                                             -0.02568                                                                           0.01292                                                                            -0.03815                                                                           0.00621                                             Lb   -0.06413                                                                            0.12254                                                                            -0.04108                                                                           0.08095                                                                            -0.01912                                          (2)    -0.04759                                                                            -0.01905                                                                           0.04255                                                                            -0.06852                                                                           -0.03545                                          (3)    0.10867                                                                             -0.07190                                                                           -0.01371                                                                           0.05029                                                                            0.04548                                           __________________________________________________________________________        K  SA5   CMA5 AST5 DIS5 PTZ5 SA7                                          __________________________________________________________________________        1  0.00000                                                                             0.00000                                                                            0.00003                                                                            0.00058                                                                            0.00013                                                                            0.00000                                        Lf                                                                              2  0.00378                                                                             -0.01177                                                                           0.00036                                                                            0.00004                                                                            -0.00079                                                                           0.00023                                          3  -0.00467                                                                            0.01264                                                                            -0.00018                                                                           -0.00005                                                                           0.00061                                                                            -0.00035                                         4  0.00003                                                                             -0.00003                                                                           0.00001                                                                            -0.00043                                                                           -0.00024                                                                           0.00000                                          5  0.00000                                                                             -0.00002                                                                           -0.00015                                                                           0.00139                                                                            -0.00003                                                                           0.00000                                          6  0.03670                                                                             -0.11819                                                                           0.00751                                                                            -0.00661                                                                           -0.00013                                                                           0.00506                                        Lb                                                                              7  -0.03092                                                                            0.09610                                                                            -0.00552                                                                           0.00477                                                                            0.00010                                                                            -0.00437                                         8  0.00066                                                                             -0.00059                                                                           -0.00011                                                                           -0.00036                                                                           -0.00021                                                                           0.00008                                          9  -0.01079                                                                            0.03259                                                                            -0.00184                                                                           0.00146                                                                            0.00039                                                                            -0.00114                                         10 -0.00095                                                                            0.00630                                                                            -0.00199                                                                           0.00210                                                                            0.00044                                                                            -0.00014                                     (1)                                                                             Lf   -0.00086                                                                            0.00083                                                                            0.00021                                                                            0.00014                                                                            -0.00028                                                                           -0.00012                                       Lb   -0.00530                                                                            0.01618                                                                            -0.00209                                                                           0.00276                                                                            0.00056                                                                            -0.00052                                     (2)    0.06153                                                                             0.00426                                                                            0.00182                                                                            -0.00011                                                                           0.00112                                                                            0.03223                                      (3)    -0.05301                                                                            -0.04412                                                                           -0.00037                                                                           0.00050                                                                            -0.00148                                                                           -0.03257                                     TOTAL  0.00235                                                                             -0.02284                                                                           -0.00043                                                                           0.00329                                                                            -0.00008                                                                           -0.00097                                     __________________________________________________________________________

Table 1 lists values of the aberrations at the wide position of the zoomlens system according to the present invention, whereas Table 2 listsvalues of the aberrations at the tele position thereof. Further,aberration coefficients of the lens units other than the first lens unitare listed as total sums of aberration coefficients characteristic ofsurfaces of these lens units. The reference symbols k(1-4) and L_(f)represent the front subunit, the reference symbols k(5-10) and L_(b)designate the rear subunit, and the reference numerals (2) and (3)denote the second lens unit and the third lens unit respectively.

It will be understood from the tables shown above that sphericalaberration which is one of the axial aberrations is little in the firstlens unit.

On the other hand, it will be understood that the astigmatism anddistortion which are the offaxial aberrations are corrected favorably inthe first lens unit. That is to say, the front subunit effectivelyovercorrects the astigmatism which is to be undercorrected by the rearsubunit and undercorrects the distortion which is to be overcorrected bythe rear subunit in the first embodiment of the present invention. Thisfact or the compensation of the functions of the rear subunit by thefront subunit can be seen from FIG. 3 illustrating a diagram wherein anoffaxial ray which is incident at a large angle on the front subunit hasa small angle of incidence on the rear subunit.

Considering the fact that it is difficult to widen a field angle of azoom lens system by using the composition of the first lens unit of theconventional zoom lens system, the present invention has modified theangle of incidence on the first lens unit to a value which facilitatesthe correction of the aberrations by arranging additional lenscomponent(s) having weak refractive power before the first lens unit soas to widen the field angle of the conventional zoom lens system asdescribed above. The additional lens component(s) and the first lensunit of the conventional zoom lens system are used as the front subunitand the rear subunit respectively which compose the new first lens unitto be used in the zoom lens system according to the present invention.Accordingly, the new first lens unit has the composition whichfacilitates the correction of the aberrations even when a zoom lenssystem has a widened field angle, and makes it possible to obtain a zoomlens system which has a wide field angle and favorably correctedaberrations. The front subunit of the first lens unit having the newcomposition may be composed of a single negative lens component, but itwill be effective for correcting the aberrations more favorably tocompose the front subunit of a negative lens component and a positivelens component.

On the other hand, in order that the first lens unit has a small outsidediameter and that the zoom lens system has an entrance pupil at alocation which is not too far from the first surface thereof, it isdesirable to configure the zoom lens system according to the presentinvention so as to satisfy the conditions to be described below.

It is desirable that the front subunit of the first lens unit comprisesat least one negative lens component and that the rear subunit comprisesat least one positive lens component and one negative lens component.

Further, it is desirable that the zoom lens system according to thepresent invention satisfies the conditions (2) through (4) mentionedbelow:

    0.1<φ.sub.1 /φ.sub.W <1.25                         (2)

    1.1<φ.sub.12W /φ.sub.W <3.0                        (3)

    1.5<β.sub.3T /β.sub.3W <4.0                      (4)

wherein the reference symbol φ_(W) represents refractive power of thezoom lens system as a whole at the wide position thereof, the referencesymbol φ₁ designates refractive power of the first lens unit, thereference symbol φ_(12W) denotes total refractive power of the firstlens unit and the second lens unit at the wide position, and thereference symbols β_(3W) and β_(3T) represent magnifications of thethird lens unit at the wide position and the tele position respectively.

The condition (2) defines the refractive power of the first lens unit.If the upper limit of the condition (2) is exceeded, it will bedifficult to correct the aberrations. If the lower limit of thecondition (2) is exceeded, it will be necessary to move the lens unitsfor long distances for zooming, thereby producing a disadvantage forcompact design of the zoom lens system according to the presentinvention.

The condition (3) is required for shortening total lengths of the firstlens unit and the second lens unit, and determining refractive powerwhich is desirable for the favorable correction of the aberrations. Ifthe upper limit of the condition (3) is exceeded, it will be impossibleto obtain sufficiently favorable optical performance of the zoom lenssystem according to the present invention though the lens system can bemade compact. If the lower limit of the condition (3) is exceeded, thezoom lens system according to the present invention will be enlarged.

The condition (4) relates to a vari-focal ratio. If the lower limit ofthe condition (4) is exceeded, it will practically be impossible toobtain a zoom lens system which has a high vari-focal ratio.

Further, when attention is paid to an axial ray and an offaxial ray, asconsidered according to the paraxial theory, which pass through thefirst lens unit, it is desirable that the zoom lens system according tothe present invention satisfies the following conditions (5) and (6):

    0.5<h.sub.B /h.sub.F <1.5                                  (5)

    0.2<AB/AF <2.0                                             (6)

wherein the reference symbol h_(F) represents a height of the axial rayincident on the front subunit of the first lens unit at the wideposition, the reference symbol h_(B) designates a height of the offaxialray incident on the rear subunit of the first lens unit at the wideposition, the reference symbol AF denotes a height of the axial rayincident on the front subunit of the first lens unit at the wideposition and the reference symbol AB represents a height of the offaxialray incident on the rear sub-unit of the first lens unit at the wideposition.

The condition (5) means that weak refractive power is to be imparted tothe front subunit of the first lens unit even when the field angle ofthe zoom lens system is to be widened by designing the first lens unitas an inverted telephoto type with negative refractive power imparted tothe front subunit or when positive refractive power is imparted to thefront subunit.

If the lower limit of the condition (5) is exceeded, the front subunitwill have a weak function for correcting the offaxial aberrations at thewide position. If the upper limit of the condition (5) is exceeded, thefront subunit will have too weak refractive power and must comprise anincreased number of lens components for correcting the aberrations,thereby enlarging the zoom lens system as a whole.

The condition (6) has significance which is similar to that of thecondition (5). If the lower limit of the condition (6) is exceeded, thefront subunit will have strong refractive power. If the upper limit ofthe condition (6) is exceeded, it will be difficult to correct theaberrations at the wide position.

The conditions (5) and (6) are to be satisfied for facilitating thecorrection of the aberrations by narrowing the angle of incidence of theoffaxial ray on the first lens unit. In other words, when theseconditions are not satisfied, the aberration correcting functions willbe effective so far as the zoom lens system has a field angle at thewide position which is close to that of an ordinary telephoto type lenssystem but the offaxial aberrations will be corrected with lens effectat the super wide angle of the zoom lens system according to the presentinvention.

Though description has been made above of a concept for composing thezoom lens system which consists of the three lens units, this concept isapplicable also to a zoom lens system which comprises four lens units.That is to say, it is possible to obtain a zoom lens systemaccomplishing the object of the present invention by: composing the zoomlens system, in order from the object side, of a first lens unit havingpositive refractive power, a second lens unit having positive refractivepower, a third lens unit having positive refractive power and a fourthlens unit having negative refractive power as shown in FIG. 2;configuring the lens system so as to perform variation of focal lengthby varying an airspace reserved between the first lens unit and thesecond lens unit, an airspace reserved between the second lens unit andthe third lens unit, and an airspace reserved between the third lensunit and the fourth lens unit; and composing the first lens unit of afront subunit and a rear subunit so as to permit widening a field angleof the lens system and satisfy the condition (1).

Refracting conditions of the thin lens component and thick lenscomponents arranged in the first lens unit are illustrated in FIGS. 4, 5and FIGS. 6 and 7 respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram illustrating a fundamental composition of thezoom lens system according to the present invention which comprisesthree lens units;

FIG. 2 shows a diagram illustrating a fundamental composition of thezoom lens system according to the present invention which comprises fourlens units;

FIG. 3 shows a diagram illustrating conditions of incidence of theoffaxial ray on the front subunit and the rear subunit of the first lensunit arranged in the zoom lens system according to the presentinvention;

FIG. 4 shows a diagram illustrating conditions of rays, as consideredaccording to the paraxial theory, refracted by the first lens unit atthe wide position;

FIG. 5 shows a diagram illustrating conditions of the rays, asconsidered according to the paraxial theory, refracted by the first lensunit at the tele position;

FIG. 6 shows a diagram illustrating conditions of rays refracted by thethick lens components of the first lens unit at the wide position;

FIG. 7 shows a diagram illustrating conditions of rays refracted by thethick lens components of the first lens unit at the tele position;

FIG. 8 through FIG. 13 show sectional views illustrating compositions ofa first embodiment through a sixth embodiment of the zoom lens systemaccording to the present invention;

FIG. 14 shows graphs illustrating aberration characteristics of thefirst embodiment for an object located at infinite distance at the wideposition thereof;

FIG. 15 shows graphs illustrating aberration characteristics of thefirst embodiment for an object located at a distance of 2.0 m at thewide position thereof;

FIG. 16 shows graphs illustrating aberration characteristics of thefirst embodiment for the objected located at infinite distance at anintermediate focal length thereof;

FIG. 17 shows graphs illustrating aberration characteristics of thefirst embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 18 shows graphs illustrating aberration characteristics of thefirst embodiment for the object located at the infinite distance at thetele position thereof;

FIG. 19 shows graphs illustrating aberration characteristics of thefirst embodiment for the object located at the distance of 2.0 m at thetele position thereof;

FIG. 20 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the infinite distance at thewide position thereof;

FIG. 21 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the distance of 2.0 m at thewide position thereof;

FIG. 22 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the infinite distance at theintermediate focal length thereof;

FIG. 23 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 24 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the infinite distance at thetele position thereof;

FIG. 25 shows curves illustrating aberration characteristics of thesecond embodiment for the object located at the distance of 2.0 m at thetele position thereof;

FIG. 26 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the infinite distance at thewide position thereof;

FIG. 27 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the distance of 2.0 m at thewide position thereof;

FIG. 28 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the infinite distance at theintermediate focal length thereof;

FIG. 29 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 30 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the infinite distance at thetele position thereof;

FIG. 31 shows graphs illustrating aberration characteristics of thethird embodiment for the object located at the distance of 2.0 m at thetele position thereof;

FIG. 32 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the infinite distance at thewide position thereof;

FIG. 33 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the distance of 2.0 m at thewide position thereof;

FIG. 34 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the infinite distance at theintermediate focal length thereof;

FIG. 35 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 36 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the infinite distance at thetele position thereof;

FIG. 37 shows curves illustrating aberration characteristics of thefourth embodiment for the object located at the distance of 2.0 m at thetele position thereof;

FIG. 38 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the infinite distance at thewide position thereof;

FIG. 39 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the distance of 2.0 m at thewide position thereof;

FIG. 40 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the infinite distance at theintermediate focal length thereof;

FIG. 41 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 42 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the infinite distance at thetele position thereof;

FIG. 43 shows graphs illustrating aberration characteristics of thefifth embodiment for the object located at the distance of 2.0 m at thetele position thereof;

FIG. 44 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the infinite distance at thewide position thereof;

FIG. 45 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the distance of 2.0 m at thewide position thereof;

FIG. 46 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the infinite distnce at theintermediate focal length thereof;

FIG. 47 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the distance of 2.0 m at theintermediate focal length thereof;

FIG. 48 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the infinite distance at thetele position thereof; and

FIG. 49 shows curves illustrating aberration characteristics of thesixth embodiment for the object located at the distance of 2.0 m at thetele position thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the zoom lens system according to the present invention will bedescribed more detailedly below with reference to the preferredembodiments illustrated in the accompanying drawings and given in a formof the following numerical data:

    ______________________________________                                        Embodiment 1                                                                  f = 28.90˜102.00 mm, F/4.5˜F/7.625                                2ω = 73.64°˜23.94°                                  r.sub.1 = 160.7804                                                               d.sub.1 = 1.2000                                                                         n.sub.1 = 1.74100                                                                           ν.sub.1 = 52.68                                r.sub.2 = 34.8076                                                                d.sub.2 = 6.9850                                                           r.sub.3 = 38.8887                                                                d.sub.3 = 3.3406                                                                         n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                r.sub.4 = 142.7690                                                               d.sub.4 = D1                                                               r.sub.5 = -194.6240                                                              d.sub.5 = 1.0000                                                                         n.sub.3 = 1.83400                                                                           ν.sub.3 = 37.16                                r.sub.6 = 38.0459                                                                d.sub.6 = 0.3520                                                           r.sub.7 = 43.6383                                                                d.sub.7 = 3.4187                                                                         n.sub.4 = 1.65844                                                                           ν.sub.4 = 50.86                                r.sub.8 = -730.7292                                                              d.sub.8 =  0.1500                                                          r.sub.9 = 32.2002                                                                d.sub.9 = 5.2460                                                                         n.sub.5 = 1.51823                                                                           ν.sub.5 = 58.96                                r.sub.10 = -96.2536                                                              d.sub.10 = D2                                                              r.sub.11 = -498.7110                                                             d.sub.11 = 1.0000                                                                        n.sub.6 = 1.78590                                                                           ν.sub.6 = 44.18                                r.sub.12 = 15.0840                                                               d.sub.12 = 0.8410                                                          r.sub.13 = 24.1630                                                               d.sub.13 = 2.7640                                                                        n.sub.7 = 1.78470                                                                           ν.sub.7 = 26.22                                r.sub.14 = -102.9802                                                             d.sub.14 = 3.9120                                                          r.sub.15 = -14.3361                                                              d.sub.15 = 1.1100                                                                        n.sub.8 = 1.65830                                                                           ν.sub.8 = 53.44                                r.sub.16 = -16.3753                                                              d.sub.16 = 4.9610                                                          r.sub.17 = ∞ (stop)                                                        d.sub.17 = 3.6000                                                          r.sub.18 =  -79.9489                                                             d.sub.18 = 2.1300                                                                        n.sub.9 = 1.66680                                                                           ν.sub.9 = 33.04                                r.sub.19 = -51.9241                                                              d.sub.19 = 0.5000                                                          r.sub.20 = -555.5860                                                             d.sub.20 = 3.0490                                                                        n.sub.10 = 1.51454                                                                          ν.sub.10 = 54.69                               r.sub.21 = -26.8298                                                              d.sub.21 = 0.1200                                                          r.sub.22 = 103.1734                                                              d.sub.22 = 0.6500                                                                        n.sub.11 = 1.80518                                                                          ν.sub.11 = 25.43                               r.sub.23 = 17.2071                                                               d.sub.23 = 5.4150                                                                        n.sub.12 = 1.60729                                                                          ν.sub.12 = 59.38                               r.sub.24 = -26.0457                                                              d.sub.24 = 1.2500                                                          r.sub.25 = -21.6894                                                              d.sub.25 = 0.8780                                                                        n.sub.13 = 1.77250                                                                          ν.sub.13 = 49.66                               r.sub.26 = -22.7792                                                              d.sub.26  = D3                                                             r.sub.27 = -54.8870                                                              d.sub.27 = 3.3170                                                                        n.sub.14 = 1.78472                                                                          ν.sub.14 = 25.71                               r.sub.28 = -22.2644                                                              d.sub.28 = 2.4970                                                          r.sub.29 = -15.6872 (aspherical surface)                                         d.sub.29 = 0.3600                                                                        n.sub.15 = 1.52492                                                                          ν.sub.15 = 51.77                               r.sub.30 = -16.8658                                                              d.sub.30 = 1.3200                                                                        n.sub.16 = 1.77250                                                                          ν.sub.16 = 49.66                               r.sub.31 = 62.5760                                                            aspherical surface coefficient                                                P = 1.0000, E = 0.30618 × 10.sup.-4, F = 0.10777 × 10.sup.-6      G = -0.18514 × 10.sup.-9, H = 0.20423 × 10.sup.-11                f       28.90         54.44   102.00                                          D1      1.750         1.750   1.750                                           D2      1.500         16.298  22.421                                          D3      15.852        7.073   1.530                                           |φ.sub.f /φ.sub.1 | = 0.65194, φ .sub.1         /φ.sub.W = 0.246, φ.sub.12W /φ.sub.W = 1.330                      h.sub.B /h.sub.F = 1.1256, AB/AF = 0.8117, β.sub.3T /β.sub.3W =     3.0                                                                           Embodiment 2                                                                  f = 28.92˜102.02 mm, F/4.5˜F/7.625,                               2ω = 73.6°˜23.94°                                   r.sub.1 = -82.5283                                                               d.sub.1 = 1.2500                                                                         n.sub.1 = 1.74100                                                                           ν.sub.1 = 52.68                                r.sub.2 = 8479.1527                                                              d.sub.2 = 1.0288                                                           r.sub.3 = 109.7348                                                               d.sub.3 = 2.2603                                                                         n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                r.sub.4 = -234.4198                                                              d.sub.4 = 0.7500                                                           r.sub.5 = -104.1899                                                              d.sub.5 = 0.8500                                                                         n.sub.3 = 1.83400                                                                           ν.sub.3 = 37.16                                r.sub.6 = 35.3417                                                                d.sub.6 = 0.3000                                                           r.sub. 7 = 39.3253                                                               d.sub.7 = 4.5192                                                                         n.sub.4 = 1.65844                                                                           ν.sub.4 = 50.86                                r.sub.8 = -20126.4985                                                            d.sub.8 = 0.1200                                                           r.sub.9 = 38.2462                                                                d.sub.9 = 5.5542                                                                         n.sub.5 = 1.65830                                                                           ν.sub.5 = 53.44                                r.sub.10 = -81.9930                                                              d.sub.10 = D1                                                              r.sub.11 = 161.3593                                                              d.sub.11 = 0.5000                                                                        n.sub.6 = 1.78590                                                                           ν.sub.6 = 44.18                                r.sub.12 = 12.1902                                                               d.sub.12 = 0.7721                                                          r.sub.13 = 20.1078                                                               d.sub.13 = 3.1941                                                                        n.sub.7 = 1.78470                                                                           ν.sub.7 = 26.22                                r.sub.14 = -324.9518                                                             d.sub.14 = 2.9127                                                          r.sub.15 = -12.2940                                                              d.sub.15 = 0.6569                                                                        n.sub.8 = 1.65830                                                                           ν.sub.8  = 53.44                               r.sub.16 = -14.2480                                                              d.sub.16 = 2.5569                                                          r.sub.17 = ∞ (stop)                                                        d.sub.17 = 3.4906                                                          r.sub.18 = -39.4065                                                              d.sub.18 = 1.9818                                                                        n.sub.9 = 1.59270                                                                           ν.sub.9 = 35.29                                r.sub.19 = -23.5086                                                              d.sub.19 = 1.0128                                                          r.sub.20 = -77.1442                                                              d.sub.20 = 2.2237                                                                        n.sub.10 = 1.50137                                                                          ν.sub.10 = 56.40                               r.sub.21 = -27.3780                                                              d.sub.21 = 0.1200                                                          r.sub.22 = 71.2472                                                               d.sub.22 = 0.8500                                                                        n.sub.11 = 1.84666                                                                          ν.sub.11 = 23.78                               r.sub.23 = 17.8516                                                               d.sub.23 = 4.0993                                                                        n.sub.12 = 1.60881                                                                          ν.sub.12 = 58.94                               r.sub.24 = -19.8521                                                              d.sub.24 = 0.8500                                                          r.sub.25 = -20.0533                                                              d.sub.25 = 1.5717                                                                        n.sub.13 = 1.77250                                                                          ν.sub.13 = 49.66                               r.sub.26 = -21.5906                                                              d.sub.26 = D2                                                              r.sub.27 = -49.9729                                                              d.sub.27 = 3.4179                                                                        n.sub.14 = 1.78472                                                                          ν.sub.14 = 25.71                               r.sub.28 = -20.4693                                                              d.sub.28 = 2.6530                                                          r.sub.29 = -13.9632 (aspherical surface)                                         d.sub.29 = 0.1000                                                                        n.sub.15 = 1.52492                                                                          ν.sub.15 = 51.77                               r.sub.30 = -14.0500                                                              d.sub.30 = 0.9444                                                                        n.sub.16 = 1.78590                                                                          ν.sub.16 = 44.18                               r.sub.31 = 57.0622                                                            aspherical surface coefficient                                                P = 1.0000, E = 0.46567 × 10.sup.-4, F = 0.16608 × 10.sup.-6      G = -0.40245 × 10.sup.-9, H =  0.76140 × 10.sup.-11               f       28.92         54.39   102.02                                          D1      1.250         15.540  20.970                                          D2      12.853        5.873   1.207                                           |φ.sub.f /φ.sub.1 | = 0.17379, φ.sub.1          /φ.sub.W = 0.304, φ.sub.12W /φ.sub.W = 1.404                      h.sub.B /h.sub.F = 1.0233, AB/AF = 0.9179, β.sub.3T /β.sub.3W =     3.329                                                                         Embodiment 3                                                                  f = 24.50˜76.49 mm, F/4.5˜F/7.5,                                  2ω = 82.88°˜31.58°                                  r.sub.1 = 96.5532                                                                d.sub.1 = 1.2000                                                                         n.sub.1 = 1.69350                                                                           ν.sub.1 = 53.23                                r.sub.2 = 27.7448                                                                d.sub.2 = 11.6550                                                          r.sub.3 = -91.4665                                                               d.sub.3 = 1.2066                                                                         n.sub.2 = 1.78470                                                                           ν.sub.2 = 26.22                                r.sub.4 = -303.5278                                                              d.sub.4 = 0.1500                                                           r.sub.5 = 39.5053                                                                 d.sub.5 = 3.0500                                                                        n.sub.3 = 1.58913                                                                           ν.sub.3 = 60.97                                r.sub.6 = 72.7943                                                                d.sub.6 = 0.1500                                                           r.sub.7 = 37.1151                                                                d.sub.7 = 5.0200                                                                         n.sub.4 = 1.60311                                                                           ν.sub.4 = 60.70                                r.sub.8 = -206.3245                                                              d.sub.8 = D1                                                               r.sub.9 = 57.4357                                                                d.sub.9 = 1.0000                                                                         n.sub.5 = 1.67790                                                                           ν.sub.5 = 55.33                                r.sub.10 = 16.3022 (aspherical surface)                                          d.sub.10 = 1.5109                                                          r.sub.11 = 36.9971                                                               d.sub.11 = 2.7640                                                                        n.sub.6 = 1.72151                                                                           ν.sub.6 = 29.24                                r.sub.12  = -33.4657                                                             d.sub.12  = 1.1015                                                         r.sub.13  = -23.8559                                                             d.sub.13  = 1.1100                                                                       n.sub.7 = 1.83400                                                                           ν.sub.7  =  37.16                              r.sub.14  = -125.8813                                                            d.sub.14  = 4.7035                                                         r.sub.15  = ∞ (stop)                                                       d.sub.15  = 3.4988                                                         r.sub.16  = -21.5971                                                             d.sub.16  = 2.1300                                                                       n.sub.8  = 1.46450                                                                          ν.sub.8  = 65.94                               r.sub.17  = -22.7796                                                             d.sub.17  = 3.9083                                                         r.sub.18  = -54.9728                                                             d.sub.18  = 2.5000                                                                       n.sub.9  = 1.51821                                                                          ν.sub.9  = 65.04                               r.sub.19  = -18.0505                                                             d.sub.19  = 0.1200                                                         r.sub.20  = 52.5661                                                              d.sub.20  = 0.8500                                                                       n.sub.10  = 1.84666                                                                         ν.sub.10  = 23.78                              r.sub.21  = 21.2304                                                              d.sub.21  = 4.0000                                                                       n.sub.11  = 1.56873                                                                         ν.sub.11  = 63.16                              r.sub.22  = -58.4819                                                             d.sub.22  = 0.8950                                                         r.sub.23  =  70.2181                                                             d.sub.23  = 2.5000                                                                       n.sub.12  = 1.77250                                                                         ν.sub.12  = 49.66                              r.sub.24  = -204.8691                                                            d.sub.24 = D2                                                              r.sub.25 = -76.9580                                                              d.sub.25 = 3.3170                                                                        n.sub.13 = 1.74000                                                                          ν.sub.13 = 28.29                               r.sub.26 = -25.1526                                                              d.sub.26 = 1.2613                                                          r.sub.27 = -19.5931 (aspherical surface)                                         d.sub.27 = 0.3600                                                                        n.sub.14 = 1.52492                                                                          ν.sub.14 = 51.77                               r.sub.28 = -23.2468                                                              d.sub.28 = 1.3200                                                                        n.sub.15 = 1.77250                                                                          ν.sub.15 = 49.66                               r.sub.29 = 35.1917                                                            aspherical surface coefficient                                                (10th surface)                                                                          P = 1.0000, E = 0.15173 × 10.sup.-4                                     F = 0.18351 × 10.sup.-6, G = -0.10833 × 10.sup.-8                 H = 0.28490 × 10.sup.-10                                      (27th surface)                                                                          P = 1.0000, E = 0.22735 × 10.sup.-4                                     F = 0.29706 × 10.sup.-7, G = -0.30210 × 10.sup.-9                 H = 0.83428 × 10.sup.-12                                      f       24.50         45.02   76.49                                           D1      0.850         16.915  22.361                                          D2      12.830        5.031   0.510                                           |φ.sub.f /φ.sub.1 | = 2.13856, φ.sub.1          /φ.sub.W = 0.175, φ.sub.12W /φ.sub.W = 1.365                      h.sub.B /h.sub.F = 1.2347, AB/AF = 0.5986, β.sub.3T /β.sub.3W =     2.727                                                                         Embodiment 4                                                                  f = 29.01˜105.43 mm, F/4˜F/7.65,                                  2ω = 73.42°˜23.2°                                   r.sub.1 = 123.2807                                                               d.sub.1 = 1.2000                                                                         n.sub.1 = 1.69680                                                                           ν.sub.1 = 55.52                                r.sub.2 = 28.1453                                                                d.sub.2 = 7.0560                                                           r.sub.3 = 31.7325                                                                d.sub.3 = 5.4876                                                                         n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                r.sub.4 = 302.3165                                                               d.sub.4 = D1                                                               r.sub.5 = -125.1445                                                              d.sub.5 = 1.0000                                                                         n.sub.3 = 1.83400                                                                           ν.sub.3 = 37.16                                r.sub.6 = 33.3387                                                                d.sub.6 = 0.6923                                                           r.sub.7 = 40.6740                                                                d.sub.7 = 3.6156                                                                         n.sub.4 = 1.65844                                                                           ν.sub.4 = 50.86                                r.sub.8 = -1157.9848                                                             d.sub.8 = 0.1500                                                           r.sub.9 = 32.3632                                                                d.sub.9 = 5.6348                                                                         n.sub.5 = 1.51823                                                                           ν.sub.5 = 58.96                                r.sub.10 = -60.9035                                                              d.sub.10 = D2                                                              r.sub.11 = -87.8043                                                              d.sub.11 = 1.0000                                                                        n.sub.6 = 1.78590                                                                           ν.sub.6 = 44.18                                r.sub.12 = 16.2024                                                               d.sub.12 = 0.9097                                                          r.sub.13 = 31.3832                                                               d.sub.13 = 2.9131                                                                        n.sub.7 = 1.78470                                                                           ν.sub.7 = 26.22                                r.sub.14 = -49.7711                                                              d.sub.14 = 3.5341                                                          r.sub.15 = -18.0019                                                              d.sub.15 = 1.2081                                                                        n.sub.8 = 1.65830                                                                           ν.sub.8 = 53.44                                r.sub.16 = -22.3951                                                              d.sub.16 = 4.7231                                                          r.sub.17 = ∞ (stop)                                                        d.sub.17 = 3.4676                                                          r.sub.18 = -115.0000                                                             d.sub.18 = 2.1300                                                                        n.sub.9 = 1.68893                                                                           ν.sub.9 = 31.08                                r.sub.19 = -64.5600                                                              d.sub.19 = 0.5000                                                          r.sub.20 = 484.4333                                                              d.sub.20 = 3.3939                                                                        n.sub.10 = 1.54739                                                                          ν.sub.10 = 53.55                               r.sub.21 = -26.1713                                                               d.sub.21 = 0.5903                                                         r.sub.22 = 146.1389                                                              d.sub.22 = 0.4350                                                                        n.sub.11 = 1.78472                                                                          ν.sub.11 = 25.71                               r.sub.23 = 17.3114                                                               d.sub.23 = 5.4869                                                                        n.sub.12 = 1.58313                                                                          ν.sub.12 = 59.36                               r.sub.24 = -25.9767                                                              d.sub.24 = 1.2500                                                          r.sub.25 = -19.9068                                                              d.sub.25 = 1.4830                                                                        n.sub.13 = 1.74100                                                                          ν.sub.13 = 52.68                               r.sub.26 = -20.9013                                                              d.sub.26 = D3                                                              r.sub.27 = -38.0869                                                              d.sub.27 = 2.7902                                                                        n.sub.14 = 1.84666                                                                          ν.sub.14 = 23.78                               r.sub.28 = -21.4684                                                              d.sub.28 = 2.6534                                                          r.sub.29 = -16.2903 (aspherical surface)                                         d.sub.29 = 0.3593                                                                        n.sub.15 = 1.52492                                                                          ν.sub. 15 = 51.77                              r.sub.30 = -17.4211                                                              d.sub.30 = 1.3500                                                                        n.sub.16 = 1.77250                                                                          ν.sub.16 = 49.66                               r.sub.31 = 82.1742                                                            aspherical surface coefficient                                                P = 1.0000, E = 0.20587 × 10.sup.-4, F = 0.86201 × 10.sup.-7      G = -0.48242 × 10.sup.-9, H = 0.27293 × 10.sup.-11                f       29.01         54.44   105.43                                          D1      1.750         1.750   1.750                                           D2      1.500         15.621  21.576                                          D3      17.439        8.661   2.636                                           |φ.sub.f /φ.sub.1 | = 0.18545, φ.sub.1          /φ.sub.W = 0.322, φ.sub.12W /φ.sub.W = 1.349                      h.sub.B /h.sub.F = 1.134, AB/AF = 0.8547, β.sub.3T /β.sub.3W =      2.973                                                                         Embodiment 5                                                                  f = 29.51˜131.00 mm, F/4.5˜F/8.25,                                2ω = 72.48°˜18.76°                                  r.sub.1 = 147.7015                                                               d.sub.1 = 0.8500                                                                         n.sub.1 = 1.74100                                                                           ν.sub.1 = 52.68                                r.sub.2 = 39.8775                                                                d.sub.2 = 6.9732                                                           r.sub.3 = 34.9579                                                                d.sub.3 = 4.4400                                                                         n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                r.sub.4 = -509.1641                                                              d.sub.4 = D1                                                               r.sub.5 = -55.5614                                                               d.sub.5 = 0.8600                                                                         n.sub.3 = 1.83400                                                                           ν.sub.3 = 37.16                                r.sub.6 = 38.7196                                                                d.sub.6 = 0.3489                                                           r.sub.7 = 45.0582                                                                d.sub.7 = 3.6100                                                                         n.sub.4 = 1.65844                                                                           ν.sub.4 = 50.86                                r.sub.8 = -134.9701                                                              d.sub.8 = 0.1200                                                           r.sub.9 = 36.3870                                                                d.sub.9 = 4.4600                                                                         n.sub.5 = 1.50137                                                                           ν.sub.5 = 56.40                                r.sub.10 = -55.5290                                                               d.sub.10 = D2                                                             r.sub.11 = -74.3691                                                              d.sub.11 = 0.5500                                                                        n.sub.6 = 1.78590                                                                           ν.sub.6 = 44.18                                r.sub.12 = 15.5103                                                               d.sub.12 = 0.734I                                                          r.sub.13 = 24.6834                                                               d.sub.13 = 2.6600                                                                        n.sub.7 = 1.78470                                                                           ν.sub.7 = 26.22                                r.sub.14 = -63.3984                                                              d.sub.14 = D3                                                              r.sub.15 = -13.9591                                                              d.sub.15 = 0.9163                                                                        n.sub.8 = 1.65830                                                                           ν.sub.8 = 53.44                                r.sub.16 = -16.2221                                                              d.sub.16 = 4.3715                                                          r.sub.17 = ∞ (stop)                                                        d.sub.17 = 3.3080                                                          r.sub.18 = -77.7267                                                              d.sub.18 = 1.7100                                                                        n.sub.9 = 1.66680                                                                           ν.sub.9 = 33.04                                r.sub.19 = -56.3440                                                              d.sub.19  = 0.1400                                                         r.sub.20 = -322.6649                                                             d.sub.20 = 2.3300                                                                        n.sub.10 = 1.50137                                                                          ν.sub.10 = 56.40                               r.sub.21 = -24.8971                                                              d.sub.21 = 0.1200                                                          r.sub.22 = 74.2271                                                               d.sub.22 = 0.5300                                                                        n.sub.11 = 1.80518                                                                          ν.sub.11 = 25.43                               r.sub.23 = 17.1956                                                               d.sub.23 = 5.1000                                                                        n.sub.12 = 1.60311                                                                          ν.sub.12 = 60.70                               r.sub.24 = -24.4180                                                              d.sub.24 = 1.0490                                                          r.sub.25 = -20.8299                                                              d.sub.25 = 0.8800                                                                        n.sub.13 = 1.77250                                                                          ν.sub.13 = 49.66                               r.sub.26 = -22.2142                                                              d.sub.26 = D4                                                              r.sub.27 = -50.1298                                                              d.sub.27 = 3.2000                                                                        n.sub.14 = 1.78472                                                                          ν.sub.14 = 25.71                               r.sub.28 = - 21.5995                                                             d.sub.28 = 2.3876                                                          r.sub.29 = -14.9318 (aspherical surface)                                         d.sub.29 = 0.4500                                                                        n.sub.15 = 1.52492                                                                          ν.sub.15 = 51.77                               r.sub.30 = -15.1591                                                              d.sub.30 = 1.1900                                                                        n.sub.16 = 1.77250                                                                          ν.sub.16 = 49.66                               r.sub.31 = 52.7870                                                            aspherical surface coefficient                                                P = 1.0000, E = 0.45142 × 10.sup.-4, F = 0.15406 × 10.sup.-6      G = -0.58035 × 10.sup.-9, H = 0.42319 × 10.sup.-11                f       29.51         62.50   131.00                                          D1      1.460         1.460   1.460                                           D2      0.766         17.061  22.292                                          D3      4.073         3.798   3.630                                           D4      15.086        6.568   1.369                                           |φ.sub.f /φ.sub.1 | = 0.34602, φ.sub.1          /φ.sub.W = 0.360, φ.sub.12W /φ.sub.W = 1.385                      h.sub.B /h.sub.F = 1.0767, AB/AF = 0.9845, β.sub.3T /β.sub.3W =     3.442                                                                         Embodiment 6                                                                  f = 29.30˜102.00 mm, F/4.6˜F/7.65,                                2ω = 72.88°˜23.94°                                  r.sub.1 = -60.5111                                                               d.sub.1 = 1.2500                                                                         n.sub.1 = 1.74100                                                                           ν.sub.1 = 52.68                                r.sub.2 = -103.1603                                                              d.sub.2 = 0.2000                                                           r.sub.3 = 51.3114                                                                d.sub.3 = 2.6500                                                                         n.sub.2 = 1.53172                                                                           ν.sub.2 = 48.90                                r.sub.4 = 254.0371                                                               d.sub.4 = 1.0500                                                           r.sub.5 = -148.9276                                                              d.sub.5 = 0.8500                                                                         n.sub.3 = 1.83400                                                                           ν.sub.3 = 37.16                                r.sub.6 = 27.9011                                                                d.sub.6 = 0.3000                                                           r.sub.7 = 28.5843                                                                d.sub.7 = 4.0000                                                                         n.sub.4 = 1.65844                                                                           ν.sub.4 = 50.86                                r.sub.8 = 451.3443                                                                d.sub.8 = 0.1200                                                          r.sub.9 = 47.3480                                                                d.sub.9 = 4.0500                                                                         n.sub.5 = 1.65830                                                                           ν.sub.5 = 53.44                                r.sub.10 = -73.2687                                                              d.sub.10 = D1                                                              r.sub.11 = -192.7657                                                             d.sub.11 = 0.5000                                                                        n.sub.6 = 1.78590                                                                           ν.sub.6 = 44.18                                r.sub.12 = 11.3110                                                               d.sub.12 = 0.6696                                                          r.sub.13 = 21.2161                                                               d.sub.13 = 1.9980                                                                        n.sub.7 = 1.78470                                                                           ν.sub.7 = 26.22                                r.sub.14 = -75.8136                                                              d.sub.14 = 5.3056                                                          r.sub.15 = ∞ (stop)                                                        d.sub.15 = 3.6513                                                          r.sub.16 = -18.5732                                                              d.sub.16 = 2.1356                                                                        n.sub.8 = 1.59551                                                                           ν.sub.8 = 39.21                                r.sub.17 = -19.9100                                                              d.sub.17 =  0.5046                                                         r.sub.18 = -31.4506                                                              d.sub.18 = 1.5121                                                                        n.sub.9 = 1.50137                                                                           ν.sub.9 = 56.40                                r.sub.19 = -18.2746                                                              d.sub.19 = 0.1200                                                          r.sub.20 = 75.5019                                                               d.sub.20 = 0.8500                                                                        n.sub.10 = 1.84666                                                                          ν.sub.10 = 23.78                               r.sub.21 = 19.0505                                                               d.sub.21 = 3.9996                                                                        n.sub.11 = 1.60881                                                                          ν.sub.11 = 58.94                               r.sub.22 = -17.4005                                                              d.sub.22 = D2                                                              r.sub.23 = -45.2876                                                              d.sub.23 = 3.0000                                                                        n.sub.12 = 1.78472                                                                          ν.sub.12 = 25.71                               r.sub.24 = -18.7253                                                              d.sub.24 = 2.6527                                                          r.sub.25 = -12.9546 (aspherical surface)                                         d.sub.25 = 0.1000                                                                        n.sub.13 = 1.52492                                                                          ν.sub.13 = 51.77                               r.sub. 26 = -14.0500                                                             d.sub.26 = 1.0000                                                                        n.sub.14 = 1.79952                                                                          ν.sub.14 = 42.24                               r.sub.27 = 119.6924                                                           aspherical surface coefficient                                                P = 1.0000, E = 0.37563 × 10.sup.-4, F = 0.36933 × 10.sup.-6      G = -0.27582 × 10.sup.-8, H = 0.24748 × 10.sup.-10                f       29.30         54.52   102.00                                          D1      1.136         13.805  20.500                                          D2      15.118        6.870   0.998                                           |φ.sub.f /φ.sub.1 | = 0.25624, φ.sub.1          /φ.sub.W = 0.385, φ.sub.12W /φ.sub.W = 1.346                      h.sub.B /h.sub.F = 0.9986, AB/AF = 1.0469, β.sub.3T /β.sub.3W =     2.651                                                                         ______________________________________                                    

wherein the reference symbols r₁, r₂, . . . represent radii of curvatureon respective lens elements, the reference symbols d₁, d₂, . . .designate thicknesses of the respective lens elements and airspacesreserved therebetween, the reference symbols n₁, n₂, .. . denoterefractive indices of the respective lens elements, and the referencesymbols ν₁, ν₂, . . . represent Abbe's numbers of the respective lenselements.

The first embodiment is a wide angle zoom lens system which has focallength f from 29.0 to 105 mm and has a composition illustrated in FIG.8.

The zoom lens system preferred as the first embodiment has a totallength which is not shortened so remarkably, or a little shorter than 90mm at the wide position thereof, and features favorable opticalperformance which is stable over the entire vari-focal range. Aberrationcharacteristics of the first embodiment are visualized in FIG. 14through FIG. 19.

The second embodiment is a wide angle zoom lens system which has focallength f from 28.9 to 102 mm and a composition shown in FIG. 9. Unlikethefirst embodiment, the second embodiment comprises a lens elementwhich is arranged in the second lens unit for correcting an imagesurface. As a result, the second embodiment has a total length which isprolonged a little.

Aberration characteristics of the second embodiment are illustrated inFIG.20 through FIG. 25.

The third embodiment is a wide angle zoom lens system which has focallength f from 24.5 to 76.5 mm covering a range of super wide fieldangles.As shown in FIG. 10, the front subunit of the first lens unitconsists of asingle negative lens component and the second lens unit hasa characteristic composition. Further, not only the third lens unit butalsothe second lens unit comprises an aspherical surface for correctingaberrations favorably.

Aberration characteristics of the third embodiment are shown in FIG. 26through FIG. 31.

Thr fourth embodiment is a wide angle zoom lens system which has focallength f from 29.0 to 105 mm. The fourth embodiment has a compositionillustrated in FIG. 11 and features improved optical performance thoughitis relatively long in the total length thereof.

Aberration characteristics of the fourth embodiment are illustrated inFIG.32 through FIG. 37.

The fifth embodiment is a wide angle zoom lens system which has focallength f from 29.5 to 131 mm and a high vari-focal ratio. The fifthembodiment has a composition shown in FIG. 12 and consists of four lensunits. This embodiment has a shortened total length of 83.6 mm at thewideposition thereof and a back focal length of 8.92 nun.

Aberration characteristics of the fifth embodiment are visualized inFIG. 38 through FIG. 43.

The sixth embodiment is a wide angle zoom lens system which has focallength f from 29.3 to 102 mm and a total length of 68.25 mm at the wideposition thereof. The sixth embodiment has a composition illustrated inFIG. 13, wherein the first lens unit consists of a front subunit whichis composed of a negative lens element and a position lens element, anda rear subunit which is composed of a negative lens element and twopositivelens elements. Further, the sixth embodiment uses an asphericalsurface on one of lens elements which is arranged in the third lens unitand presumedto be made of a synthetic resin material. Further, the sixthembodiment hasa sufficiently long back focal length of 9.52 nun at thewide position thereof.

Aberration characteristics of the sixth embodiment are shown in FIG. 44through FIG. 49.

Though lateral chromatic aberration of the g-line is not correctedsufficiently favorably at the wide position of the sixth embodimentwhich is configured so as to have a shortened total length, the sixthembodimenthas aberrations corrected favorably as a whole. Further, thesixth embodiment has distortion which is varied relatively monotonously.Furthermore, astigmatism is curved in the meridional direction at thewideposition under an influence due to the aspherical surface used inthe thirdlens unit.

In addition, each of the embodiments which consists of three lens unitsis focused by moving the second lens unit, whereas each of theembodiments which consists of four lens units is focused by moving thesecond lens unit and the third lens unit.

In each of the embodiments other than the sixth embodiment, a lenscomponent is arranged, at a most image side location in the focusinglens unit or units, for correcting variations of aberrations caused byfocusingthe zoom lens system on an object located at a short distance,and the focusing and correction of the aberrations are performed bymoving the lens components other than the lens component mentioned abovewhich are arranged in the focusing lens unit or units.

The aspherical surfaces used in the embodiments described above haveshapeswhich are expressed by the formula shown below: ##EQU1##wherein adirection of the optical axis is taken as the x axis, adirectionperpendicular to the optical axis is taken as the y axis, thereference symbol r represents a radius of curvature as measured in thevicinity of avertex of the aspherical surface, and the reference symbolp designates a conical coefficient, and the reference symbols E, F, G,H, . . . denote aspherical surface coefficients.

The wide angle zoom lens system according to the present invention ischaracterized in the composition of the first lens unit which makes itpossible to widen a field angle of a zoom lens system, which canconventionally be widened hardly without prolonging a total length andoutside diameter thereof, while maintaining favorable opticalperformance thereof.

I claim:
 1. A wide angle zoom lens system comprising, in order from theobject side: a first lens unit having positive refractive power, asecond lens unit having positive refractive power, and a third lens unithaving negative refractive power wherein focal length is varied byvarying airspaces reserved between said lens units, and wherein saidfirst lens unit consists of a front subunit and a rear subunit, and saidfirst lens unit satisfies the following condition ( 1 ):

    |φ.sub.f /φ.sub.1 |<6.0          (1)

wherein the reference symbol φ₁ represent refractive power of said firstlens unit and the reference symbol φ_(f) designates refractive power ofsaid front subunit.
 2. A wide angle zoom lens system according to claim1 wherein the front subunit of said first lens unit consists of anegative lens component.
 3. A wide angle zoom lens system according toclaim 1 wherein the front subunit of said first lens unit comprises anegative lens component.
 4. A wide angle zoom lens system according toclaim 3 wherein said first lens unit comprises a negative lens componentand a positive lens component.
 5. A wide angle zoom lens systemaccording to claim 2 wherein said negative lens component is a negativemeniscus lens component.
 6. A wide angle zoom lens system according toclaim 1 or 2 wherein an aperture stop is arranged between a lenscomponent arranged at a most object side location in said second lensunit and a lens component arranged at a most image side location in saidsecond lens unit.
 7. A wide angle zoom lens system according to claim 1,2 or 4 wherein said rear subunit comprises a positive lens component anda negative lens component.
 8. A wide angle zoom lens system according toclaim 1 wherein said first lens unit satisfies the following condition (2 ):

    0.1<φ.sub.1 /φ.sub.W <1.25                         (2)

wherein the reference symbol φ_(W) represents refractive power of saidzoom lens system as a whole at a wide position thereof.
 9. A wide anglezoom lens system according to claim 1 wherein said first lens unit andsaid second lens unit satisfy the following condition (3):

    1.1<φ.sub.12W /φ.sub.W <3.0                        (3)

wherein the reference symbol φ_(W) represents refractive power of saidzoom lens system as a whole at the wide position, and the referencesymbol φ₁₂ w designates total refractive power of said first lens unitand said second lens unit at the wide position.
 10. A wide angle zoomlens system according to claim 1 wherein said third lens unit satisfiesthe following condition (4): 1.5<β₃T /β_(3W) <4.0 (4) wherein thereference symbols β_(3W) and β_(3T) represent magnifications of saidthird lens unit at a wide position and a tele position respectively ofsaid zoom lens system.
 11. A wide angle zoom lens system according toclaim 1 satisfying the following condition (5):

    0.5<h.sub.B /h.sub.F <1.5                                  (5)

wherein the reference symbol h_(F) represents height of an axial ray, asconsidered according to the paraxial theory, which is incident on thefront subunit of said first lens unit and the reference symbol h_(B)designates height of the axial ray which is incident on the rear subunitof said first lens unit.
 12. A wide angle zoom lens system according toclaim 1 satisfying the following condition (6):

    0.2<AB/AF<2.0                                              (6)

wherein the reference symbol AF represents height of the offaxial ray,as considered according to the paraxial theory, which is incident on thefront subunit of said first lens unit and the reference symbol ABdesignates height of the offaxial ray which is incident on the rearsubunit of said first lens unit.
 13. A wide angle zoom lens systemaccording to claim 4 wherein said negative lens component is a negativemenicus lens component.
 14. A wide angle zoom lens system according toclaim 4 wherein an aperture stop is arranged between a lens componentarranged at a most object side location in said second lens unit and alens component arranged at a most image side location in said secondlens unit.
 15. A wide angle zoom lens system according to claim 4wherein said rear subunit comprises a positive lens component and anegative lens component.